Abstract

Migratory shorebirds inhabit the shorelines of rivers, wetlands, oceans and lakes, where they need to rest and feed during their non-breeding seasons to prepare for their annual migrations to breeding grounds in the Arctic. Along their flyways many non-breeding and stop-over sites are under pressure from coastal developments, disturbance, global sea level rise and water resource development. In this thesis I investigated how migratory shorebirds responded to habitat loss in the Hunter estuary, a non-breeding site in south-eastern Australia, and how they used remaining estuarine habitats. The Hunter estuary is a wetland of international importance but has a long history of modification from industrial and urban development which began in the late 1800s. Based on recent counts (2001-07), the Hunter estuary now only supports two species in internationally significant numbers (Eastern Curlews Numenius madagascariensis and Sharp-tailed Sandpipers Calidris acuminata) compared to seven species listed from earlier records (1970-90). Overall, I detected a 42% decline in total numbers of migratory shorebirds (1981 - 2007) in the estuary, with significant declines (44 - 83%) in four species. The tidal cycle was the main driver for the distribution of shorebirds in the Hunter estuary with most species feeding in exposed intertidal mudflats at low tide and being forced to rest at high tide. Eastern Curlews roosted on artificial structures and sandbanks during the day but at night they moved to flooded saltmarshes. Shallow water was important at the roost sites, as it provided a mechanism for cooling on warm days and for detecting predators at night. Vigilance behaviour made up 30 - 40% of Eastern Curlews roosting time, but vigilance increased by about 20% prior to their migration (Feb-Mar). Day roosting habitat was most limited during spring high tides and periods of high disturbance. Disturbance was significant at the day roosts (0.8 - 1.;7 hr-1), mostly from birds of prey, but Eastern Curlews spent longer in flight after being disturbed by people. The tidal period and tide type (neap or spring) determined shorebird distribution on intertidal mudflats. Intertidal mudflats in Fullerton Cove provided important feeding habitat for many species, but artificial mudflats impounded in the North Arm of the Hunter River extended foraging time for small shorebird species which fed until the tide forced their relocation to the main day roosts. These impoundments increased in importance for all shorebirds during neap cycles and one to three hours before high tide when the availability of intertidal mudflats was limited in the rest of the Hunter estuary. Overall, a high percentage (> 90%) of Bar-tailed Godwits Limosa lapponica foraged during low tides and 50% of godwits continued to forage up to three hours after low tide. Foraging Bar-tailed Godwits were most successful in mudflats in Fullerton Cove but prey availability was not uniform among mudflats. Saltmarshes provided major night roosting habitat and important feeding habitat for small shorebird species, including Sharp-tailed Sandpipers, which foraged in saltmarsh regardless of the tidal period. Generally, most shorebird species avoided saltmarshes with large stands of mangroves, preferring sites with open saltmarsh and tidal pools. Changes in attitudes towards wetlands management in the last three decades coincided with the formal protection and rehabilitation of shorebird habitat in the Hunter estuary. In 1995, culverts were removed to restore tidal flushing to estuarine wetlands on Ash Island, a highly modified wetland complex in the Hunter estuary.;Although high inter-annual variability in migratory shorebird populations made it difficult to detect short-term responses to wetland manipulation, long-term monitoring (1994-2007) indicated that increased tidal flushing had promoted mangrove expansion indirectly reducing habitat availability for shorebirds. Mangrove removal has the potential to restore this imbalance, but further studies are needed to support an adaptive management approach to managing shorebird habitat in the Hunter estuary. The cumulative loss and degradation of estuarine habitats in south-eastern Australia and other parts of the East Asian-Australasian flyway continue to threaten shorebird populations, but these impacts could be addressed through greater commitment to the protection and active management of shorebird roosting and feeding habitats in their non-breeding range.